1. Field of the Invention:
The present invention relates to a luminous element holding structure for holding a luminous element such as a light emitting diode (hereinafter referred to as "LED") in combination with a key switch, for example, of a keyboard having a plurality of such key switches.
2. Description of the Prior Art:
A conventional key switch employing a membrane switch element is shown in FIGS. 6(A) and 6(B). The key switch is in a closed state in FIG. 6(A) and is in an open state in FIG. 6(B). In FIGS. 6(A) and 6(B), there are shown a base plate 1, a membrane switch element 2 provided on one side of the base plate 1, a tubular housing 6 having an open upper end and a bottom wall provided with a through hole, and mounted on the membrane switch element 2, a key 7 including a key head having a substantially prismoidal shape and a stem 7b projecting downward from the center of the key head and having a relatively small tip 7a, a small coil spring 8 having a relatively small diameter and having one end fitted on the tip 7a of the key 7, and a large coil spring 9 having a comparatively large diameter. The large coil spring 9 is provided in the housing 6 so that one end thereof is in contact with the lower surface of key head of the key 7 and the other end thereof is in contact with the bottom surface of the housing 6 to hold the key 7 at an upper position and to space the lower end of the small coil spring 8 from the membrane switch element 2 by a gap l.
The membrane switch element 2 comprises two flexible films 3a and 3b, a spacer 4 held between the flexible films 3a and 3b and provided with a plurality of through holes to form spaces between the flexible films 3a and 3b, a fixed contact 5a attached to the upper surface of the lower flexible film 3b, namely, the flexible film below the spacer 4, within each through hole, and a movable contact 5b disposed opposite the fixed contact 5a and attached to the lower surface of the upper flexible film 3a, namely, the flexible film over the spacer 4. The small coil spring 8 is disposed upright directly above the fixed contact 5a and the movable contact 5b.
When the key 7 is depressed, the large coil spring 9 is compressed to bring the lower end of the small coil spring 8 into contact with the flexible film 3a of the membrane switch element 2. As the key 7 is depressed further, the large coil spring 9 is compressed further and the small coil spring 8 is also compressed to apply pressure to the upper flexible film 3a. Then, the upper flexible film 3a is flexed by the small coil spring 8 into a shape as shown in FIG. 6(B), so that the movable contact 5b provided on the upper flexible film 3a opposite the fixed contact 5a is brought into contact with the fixed contact 5a to close the key switch.
When the key 7 is released, the compressed coil springs 8 and 9 are allowed to recover their original shapes, the small coil spring 8 is separated from the flexible film 3a by the gap l, the flexed flexible film 3a is allowed to recover its original shape, and thus, the movable contact 5b is separated from the fixed contact 5a to open the key switch.
There is a proposed pilot lamp structure which illuminates luminous element such as an LED to indicate the correct contact of the movable and fixed contacts of a key switch when the key of the key switch is depressed, to ensure the correct operation of a membrane keyboard having key switches including a membrane switch element having pairs of contacts which are brought into electrical contact through the component film of the membrane switch element by the keys. A conventional LED holding structure for holding an LED on such a membrane keyboard will be described hereinafter.
FIG. 7 is an exploded perspective view of a conventional LED holding structure, and FIG. 8 is a sectional view of the assembled LED holding structure of FIG. 7.
Referring to FIGS. 7 and 8, an LED 10 has two lead wires 10a vertically extending downward and each bent substantially at the middle thereof at a right angle. An LED holder 11 comprises a cruciform-shaped insulating member 12 having a head 12a, and a pair of conductive members 13 attached respectively to the opposite sides of the vertical leg of the insulating member 12 and each having a groove 13a. A holding plate 14 has holes respectively corresponding to housings 6 and keys 7. A slit 14a for receiving the head 12a of the LED holder 11 is formed in the edge of the holding plate 14 defining each such hole.
Referring to FIG. 9, in a membrane switch element 2, which is the same as the membrane switch element 2 shown in FIGS. 6(A) and 6(B), a portion of the upper flexible film 3a and a portion of the spacer 4 are removed at a predetermined position to form a hole 15 for receiving the LED holder 11. Fixed electrodes 16 are arranged in the hole 15 on the lower flexible film 3b so as to cooperate with the conductive members 13 of the LED holder 11.
To mount these parts on a base plate 1, the bent portions of the lead wires 10a of the LED 10 are inserted, respectively, in the grooves 13a of the conductive members 13 of the LED holder 11 to combine the LED 10 and the LED holder 11. Then, the head 12a of the insulating member 12 of the LED holder 11 is inserted in the slit 14a of the holding plate 14. Then, the LED holder 11 is inserted in the hole 15 formed in the membrane switch element 2 and is adhesively attached to the upper surface of the base plate 1 so that the conductive members 13 of the LED holder 11 are pressed respectively against the fixed electrodes 16 formed on the membrane switch element 2 to connect the LED 10 electrically to the fixed electrodes 16. Thus, the LED 10 is mounted on the membrane keyboard as shown in FIG. 8.
When the key 7 is depressed to close the key switch, the fixed electrodes 16 are connected to a power supply, whereby the LED 10 lights up to indicate that the key switch is positively closed.
Referring to FIGS. 10 and 11 showing another conventional LED holding structure, a pair of lead wires 17a extends downward from the luminous head of an LED 17. An LED holder 18 is formed of insulating material and has a cylindrical shape with a length smaller than the length of the lead wires 17a of the LED 17. The LED holder 18 is provided with a pair of through holes 18a for respectively receiving the lead wires 17a of the LED 17, and has a threaded hole 18b extending at a predetermined location in the lower surface thereof. A hole 19 having a shape complementary to the external shape of the LED holder 18 extends through the upper flexible film 3a and spacer 4 of a membrane switch element 2. A pair of fixed electrodes 20 are provided on the upper surface of the flexible film 3b of a membrane switch element 2, namely, at the bottom of the hole 19, so as to respectively contact the pair of lead wires 17a of the LED 17. A through hole 21 is open to the hole 19 and extends through a base plate 1 and the lower flexible film 3b of the membrane switch element 2 at a location aligned with the threaded hole 18b of the LED holder 18.
To mount the LED 17 and the LED holder 18 on the base plate 1, the lead wires 17a of the LED 17 are inserted, respectively, in the through holes 18a of the LED holder 18 and then the respective free ends of the lead wires 17a projecting from the lower surface of the LED holder 18 are bent at a right angle to combine the LED 17 and the LED holder 18. Then, the LED holder 18 is placed in the hole 19 and on the lower flexible film 3b so that the bent portions of the lead wires 17a respectively contact the fixed electrodes 20 provided on the lower flexible film 3b of the membrane switch element 2, and then a screw 22 is inserted through the through hole 21 from below the base plate 1 adhesively attached to the lower surface of the membrane switch element 2 and is screwed in the threaded hole 18b of the LED holder 18 to fasten the LED holder 18 through the membrane switch element 2 to the base plate 1. Thus, the bent portions of the lead wires 17a of the LED 17 are respectively pressed against the fixed electrodes 20 for providing an electrical connection.
Both the conventional LED holders 11 and 18 are formed of an elastic material and are pressed when mounted on the membrane switch element to provide a stable electrical connection of the lead wires of the LED and the fixed electrodes. In the conventional membrane keyboard, every key switch is not necessarily provided with an LED. Rather, only some of the key switches provided on the keyboard are provided with LEDs.
However, the foregoing conventional LED holding structures have the following drawbacks.
To combine the former conventional LED holder 11 and an LED, the lead wires of the LED have to be bent at a right angle each at the middle thereof, which contributes to an increase in the cost associated with manufacturing the structure. Furthermore, when only some of the key switches of the keyboard are to be provided with LEDs while the rest of the key switches are not, two kinds of through holes, namely, through holes each having a shape conforming to the external shape of the key and provided with the slit for receiving the head of the LED holder 11 therein and through holes each having a shape conforming only to the external shape of the key, must be punched in the holding plate 14. Therefore, two different tools are necessary for punching these different through holes. If a key switch originally not provided with an LED is required to be provided with one, the holding plate needs to be replaced with another holding plate because the through hole for the key switch is not provided with the slit for receiving the head of the LED holder. Still further, since the LED holder is loosely joined to the bracket simply by fitting the head thereof in the slit formed in the holding plate, the LED holder is liable to be dislocated when subjected to vibrations or shocks entailing faulty contact between the lead wires of the LED and the fixed electrodes.
To combine the latter conventional LED holder 18 and an LED, the free ends of the lead wires of the LED projecting from the lower surface of the LED holder need to be bent, which requires additional work contributing to the manufacturing cost thereof. Furthermore, since the fixed electrodes provided on the membrane switch element for the LED are formed of soft material such as silver or copper, the fixed electrodes are liable to be damaged by the lead wires of the LED causing an unstable electrical connection between the lead wires and the fixed electrodes. Still further, since the flexible films of the membrane switch element are polyester films or the like, it is impossible to solder the lead wires of the LED to the fixed electrodes. When the flexible films are heat-resistant films such as polyimide films, it is possible to solder the lead wires of the LED to the fixed electrodes. However, polyimide films are more expensive by far than polyester films. Moreover, fastening the LED holder to the base plate with a screw requires additional assembling work.